Bottle rockets (Air Time)

Challenge:  To design a bottle rocket to achieve maximum air time.

Parameters: The bottle rocket must have one unmodified 2L pop bottle as the pressure vessel, to which Mr. J will glue a flow restrictor (so it can be launched by my launch device).  Fins, fairing, fuselage, nose-cones, parachutes, etc. must by taped to the pressure vessel and cannot damage it in any way.  The nose cone cannot be sharp, and there can be no metal parts for safety reasons.  

Scoring:  You will be shown how to build a rocket and use the launcher, and will have two attempts to launch your rocket.  You will be charging your rocket with 100 psi air from a compressor, and will be firing the launcher by yourself.  At least three other classmates must independently measure the time interval from launch to the moment any part of your rocket hits the ground.  Your best attempt will be used for the score.  

Score = Air Time in seconds (average of at least three independent timers)

Rank will be based on score, with highest score earning highest rank.

Physics:  Unbalanced force applied by the compressed air on the escaping water causes an equal and opposite force on the pressure vessel (Newton's Third Law).  The rocket will accelerate according to Newton’s Second Law.  The force is proportional to the air pressure and varies as the rocket accelerates, decreasing during the launch.  The mass of the rocket also changes as water is expelled, which improves acceleration, so the acceleration is definitely not uniform.  After it runs out of water, the rocket will still be experiencing different unbalanced forces due to gravity and air drag.  The force of drag decreases as speed decreases, so again, not uniform acceleration.  After your first launch, you can try changing the parameters of the rocket to make it stay aloft longer.

Extensions: Physics modelling software can handle all the variables mentioned above, and you may be able to find someone who has already done that work online because this is a very popular project!

Help/Hints: Too many to mention here, but pay attention in class!  You will need lots of 2L pop bottles, tuck tape, fin material, parachute material, string, and playdoh or plasticine.

Quiz Topics: Constant Acceleration in One Dimension, Intro to Projectile Motion.

Newton’s Laws.  (Unbalanced Forces Cause Acceleration)

Online Text: ch 2, ch 4, ch 5 (one dimension and intro to two)